Support is requested for continuation of experiments in mammals aimed at determinig the functional organization of 1) the spinal terminations made by small diameter sensor fibers (A delta myelinated or unmyelinated), known to have a major part in pain and temperature sense, and 2) the spinal neurons in the dorsal horn marginal zone (MZ) and substantia gelatinosa (SG) receiving excitatory input from such sensory fibers. The proposed studies have evolved from earlier analyses of nociceptive sense organs and their spinal projections. Six sets of experiments, each proposing correlation of function features to either ultrastructural characteristics or the neural transmitters involved are to be undertaken over a five year period. The functional properties of individual dorsal root fibers and MZ and SG neurons will be determined from extracellular and intracellular electrophysiological recordings in anesthetized or decerebrate animals (cat or cynomolgus monkey). The neurons giving rise to recorded unitary potential will be functionally characterized by determining their responses to quantitatively varied mechanical and thermal stimuli and to the fiber components of graded afferent volleys. The elements from which recordings are obtained will be stained intracellularly with horseradish peroxidase or a fluorescent dye by inotophoresis from the ffne capillary recording electrodes. After histological preparation, and either histochemical reaction or exposure to the appropriate wavelength of light, the arborization of the fiber or neuron will be determined at the light microscopic level, and, in some experiments, examined subsequently by electron microscopy so that the ultrastructure of stained cells can be related to the neuronal profiles. Certain experiments propose to relate the content of putative peptide neural transmitters in marked neurons or the elements they contact by sequential immunocytochemical procedures.